Different types of tools are used to perform hundreds of processing operations during semiconductor device fabrication. Most of these operations are performed in process chambers at very low pressure, i.e., in a vacuum or partial vacuum. Such process chambers may be arranged about a central hub, and the hub and process chambers may be kept at substantially the same very low pressure. Wafers may be introduced to the process chambers by wafer handling systems that are mechanically coupled to the process chambers. The wafer handling systems transfer wafers from the factory floor to the process chamber. The wafer handling systems may include loadlocks to bring the wafers from atmospheric conditions to very low pressure conditions and back, and robots to transfer the wafers to various positions. Wafer handling systems may utilize robots which operate outside of the vacuum environment, e.g., robots which operate in the ambient factory floor environment, and robots which operate within the very low pressure environment, e.g., vacuum, of the process chambers. Throughput—the number of wafers that is processed in a period of time—is affected by the process time, the number of wafers that are processed at a time, as well as timing of the steps to introduce the wafers into the vacuum process chambers.
Conventional transfer chambers typically feature one or more robotic manipulators that are configured to rotate about a fixed point in the center of a generally circular transfer chamber. A plurality of process chambers may be connected to ports located about the periphery of this circular transfer chamber (the exterior of the transfer chamber may be octagonal or otherwise faceted to provide flat mounting surfaces for mounting the process chambers to the transfer chamber. Due to various factors, e.g., wafer size, process chamber size, and available factory floor space, the number of process chambers (and/or other chambers, e.g., loadlocks) that may be connected to a typical transfer module for a 300 mm wafer process may be limited to, for example, eight chambers—two of which are typically reserved for use by load locks. The number of available mounting locations for process and other chambers at larger wafer sizes, e.g., 450 mm wafers, may, due to common industry floor space constraints and other factors, be reduced to four or six chambers.
In some cases, two conventional transfer chambers may be connected together in an “8” configuration. This may increase the number of available facets for mounting chambers to the transfer chambers, but some of the facets may be blocked from use due to the presence of the additional transfer chamber or because the facets are used to connect the transfer chambers to each other. In such figure-8 configurations, two robot arm assemblies are used, one in each chamber, and the robot arms must pass wafers off to one another in order to move wafers between the transfer chambers.